Early motorized vehicles were little more than horse drawn carriages with a motor replacing the horses. Doors on these early vehicles were simple affairs. A single piece of material, such as wood or metal, was hinged on one side and secured with a simple latch. The mechanism was no more complicated than what currently might be used on a garden gate.
In contrast, modern motorized vehicles are infinitely more sophisticated. Not surprisingly, the doors on modern vehicles have gone well beyond their simple origins. Features like powered windows and locks and their associated controls are now considered standard as are a variety of related safety features.
The mechanism for opening the door on a modern vehicle, however, remains primarily mechanical. Handle assemblies are provided on the inside and outside of the vehicle.  These handles are linked to the latch mechanism. When pulled, the handle moves a link rod that in turn activates the door latch.
Unfortunately, in an accident involving a lateral impact the outer door handle's inertia keeps it in place, while the force of the impact moves the vehicle. This produces a relative movement of the door handle, in response to this relative movement, the link rod moves, and the door latch is actuated. This creates the potential for a number of undesirable situations during an accident: an occupant of the vehicle could be ejected; the door could open and then close on an occupant's arm or leg; accident debris could be projected into the vehicle interior; etc.
One common solution to this problem is to incorporate a weight equal in mass to the door handle to counterbalance it and overcome its inertia. Another solution involves incorporating a weighted pendulum of lesser inertia that responds to the forces generated by a lateral impact more rapidly that the door handle. On a lateral impact this weighted pendulum is effectively moved into a blocking position that immobilizes the door handle. Still another solution is to provide a latching mechanism for the door handle that must be released to open the door.
Some solutions to this problem are specifically described in the following references:                U.S. Pat. No. 3,967,844 describes a double action door handle. The first action on the handle depresses a spring that unlocks the handle  from a base member, and the second action permits actuation of the door latch.        U.S. Pat. No. 5,431,462 describes a door handle connected to the latch mechanism via a two piece linkage having a pivot point positioned below the latch assembly. Outward movement of the door is translated to press the first half of the linkage downward. This downward travel is translated through the pivot point to the second half of the linkage to actuate the latch.        U.S. Pat. Nos. 5,669,642 and 6,464,270 B1 each describe a door handle containing a pivoting weight. The weight acts has a pendulum that rotates on lateral impact to block outward travel of the door handle.        U.S. Pat. No. 6,447,030 describes a resilient finger combined with a detent. Gradual pressure on the door handle causes the detent to depress and slide around the resilient finger. On rapid lateral acceleration the detent catches on the resilient finger and prevents movement of the door handle and actuation of the door latch.        
Prior art solutions, particularly those described in described in U.S. Pat. Nos. 3,967,844; 5,669,642; 6,447,030; and 6,464,270 B1 are relatively complex, difficult and expensive to manufacture, more likely to fail, and difficult to maintain and repair. 
While the mechanism described in U.S. Pat. No. 5,432,462 appears somewhat efficient at first glance, a careful reading of this reference reveals a number of significant problems. The described mechanism is loosely fitted (see, FIG. 3 and related text). In order to adequately transmit opening force and reduce rattling during operation of the vehicle stabilizing brackets must be used (see, FIGS. 4–7 and related text). At best the described designs require complex tuning to achieve operational reliability. At worst, the described designs do not sufficiently decouple the handle's inertia from the activating arms to prevent a door from opening during lateral impact.